1. Field of the Invention
The present invention relates to a glass terminal and, more specifically, to a glass terminal used for high-speed optical communication.
2. Description of the Related Art
A lead is sealed in an metallic eyelet member with glass and a block-like optical element mounting section is uprightly mounted on the eyelet member to form a glass terminal, wherein an optical element (laser element) is mounted onto the optical element mounting section. Thus, the glass terminal is used as an optical semiconductor device by electrically connecting the lead to the optical element member. FIG. 9 illustrates a conventional glass terminal on which the optical element is mounted. In this drawing, 10 denotes an eyelet member, 12 denotes a lead which is inserted into a through-hole provided in the eyelet member 10 and sealed with glass, 14 denotes an optical element mounting section, and 16 denotes an optical element.
An optical semiconductor device in which the glass terminal is used for a communication device, using high-frequency signals, such as for optical communication. When the high-frequency signals are used, it is necessary to take the transmission characteristic of the signal into account for the purpose of matching it with a characteristic impedance of a transmission path. For this purpose, a structure of a glass terminal improved in high-frequency characteristics has been proposed. For example, as a coaxial structure having the lead as a core is formed in a portion in which the lead is inserted into the eyelet and sealed with glass, it is possible to employ a method in which the characteristic impedance is adjusted by regulating an inner diameter of the through-hole or an outer diameter of the lead in this coaxial structure portion or by covering the glass surface with a covering material having a dielectric constant different from the glass (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 6-29451).
While exclusive devices have been developed in the optical semiconductor device for using high-frequency signals, they are expensive. On the contrary, a glass terminal which can be produced at a low cost is much more suitable for mass production.
In this regard, when an extremely high-frequency signal of 10 GHz is used, impedance matching becomes impossible, in the conventional glass terminal shown in FIG. 9, even if the characteristic impedance is regulated in the coaxial structure portion of the lead 12, because the lead 12 is exposed as it is on the eyelet member 10, whereby the transmission loss of the high-frequency signal is not negligible. In the glass terminal of the conventional type, while the characteristic impedance is adjustable in a range from 15 to 25xcexa9 in a portion within the eyelet member 10, that in a portion exposed above the eyelet member 10 is approximately 200xcexa9.
Accordingly, the present invention has been made to solve these problems in the prior art.
Accordingly, an object thereof is to provide a glass terminal capable of improving the transmission characteristic of a high-frequency signal.
Another object of the present invention is to provide a glass terminal, which is excellent in the transmission characteristic of a high-frequency signal even in a lead portion extending above the eyelet member, as well as being easily produced in a mass-production system.
According to the present invention, there is provided a glass terminal for high-speed optical communication, the terminal comprising: an eyelet member provided with an inserting hole; an optical element mounting block fixed to the eyelet member, the optical element mounting block having such a size to cover a range where the inserting hole is arranged, the optical element mounting block being provided with a coaxial hole arranged coaxially with the inserting hole and having a diameter larger than that of the signal lead; a signal lead being inserted into the inserting hole and sealed with the eyelet member by means of glass filled in the inserting hole, the signal lead being extending into the coaxial hole; and the optical element mounting block having a side surface partially cut off so that an outer peripheral surface of the signal lead in said coaxial hole is partially exposed.
A side surface of the optical element mounting block is cut off as a tapered surface, so that an exposed area of the outer peripheral surface of the signal lead coaxial hole is gradually increased.
According to another aspect of the present invention, there is provided a glass terminal for high-speed optical communication, the terminal comprising: a metallic eyelet member having upper and lower surfaces and having a plurality of inserting holes extending substantially perpendicular to the upper and lower surfaces and spaced from each other; an optical element mounting block having a bottom surface fixed to the upper surface of the eyelet member, the bottom surface of the optical element mounting block having such a size to cover a range of the upper surface of the eyelet member where the plurality of inserting holes are arranged, the optical element mounting block being provided with coaxial holes arranged coaxially with the inserting holes, respectively, each of the coaxial holes having a diameter larger than that of the signal lead; the signal leads being sealed with the eyelet member by means of glass filled in the inserting holes, respectively, and extended into the respective coaxial hole; and the optical element mounting block having a side surface thereof partially cut off so that an outer peripheral surface of each of the signal leads is partially exposed.
In this case also, a side surface of the optical element mounting block is cut off as a tapered surface, so that an exposed area of the outer peripheral surface of each of the signal leads in the respective coaxial hole is gradually increased.
According to a still another object of the present invention there is provided an optical element comprises an above-mentioned glass terminal and further comprising: a substrate mounted on a surface of the optical element mounting block perpendicular to the bottom surface; and an optical element mounted on the substrate so that the optically element is electrically connected with the exposed portion of the signal leads.
The optical element mounted on the substrate is electrically connected with the exposed portion of the signal leads by means of wire-bonding.